Combined intravascular ultrasound and intravascular photoacoustic (IVUS/IVPA) imaging has been previously established as a viable means for assessing atherosclerotic plaque morphological and compositional characteristics using both endogenous and exogenous contrast. In this study, IVUS/IVPA imaging of atherosclerotic rabbit aortas following systemic injection of gold nanorods (AUNRs) with peak absorbance within the tissue optical window is performed. Ex vivo imaging results reveal a high photoacoustic signal from localized AUNRs in regions with atherosclerotic plaques. Corresponding histological staining further confirms the preferential extravasation of AUNRs in atherosclerotic regions with compromised luminal endothelium and acute inflammation. The ability to detect AUNRs using combined IVUS and photoacoustic imaging in the presence of luminal saline and luminal blood is evaluated using both spectroscopic and single wavelength IVPA imaging techniques. Results demonstrate that AUNR detection within the arterial wall can be achieved using both methods, even in the case of imaging through luminal blood.
Combined intravascular photoacoustic (IVPA) and intravascular ultrasound (IVUS) imaging has been previously
established as a viable means for imaging atherosclerotic plaques using both endogenous and exogenous contrast. In this
study, IVUS/IVPA imaging of an atherosclerotic rabbit aorta following injection of gold nanorods (AuNR) with peak
absorbance within the tissue optical window was performed. Ex-vivo imaging results revealed high photoacoustic signal
from localized AuNR. Corresponding histological cross-sections and digital photographs of the artery lumen confirmed
the presence of AuNR preferentially located at atherosclerotic regions and in agreement with IVPA signal. Furthermore,
an integrated IVUS/IVPA imaging catheter was used to image the AuNR in the presence of luminal blood. The results
suggest that AuNR allow for IVPA imaging of exogenously labeled atherosclerotic plaques with a comparatively low
background signal and without the need for arterial flushing.
Carotid atherosclerosis has been identified as a potential risk factor for cerebrovascular events, but information about its
direct effect on the risk of recurrent stroke is limited due to incomplete diagnosis. The combination of vascular
ultrasound, strain rate and spectroscopic photoacoustics could improve the timely diagnosis of plaque status and risk of
rupturing. Current ultrasound techniques can noninvasively image the anatomy of carotid arteries. The spatio-temporal
variation in displacement of different regions within the arterial wall can be derived from ultrasound radio frequency
data; therefore an ultrasound based strain rate imaging modality can be used to reveal changes in arterial mechanical
properties. Additionally, spectroscopic photoacoustic imaging can provide information on the optical absorption
properties of arterial tissue and it can be used to identify the location of specific tissue components, such as lipid pools.
An imaging technique combining ultrasound, strain rate and spectroscopic photoacoustics was tested on an excised
atherosclerotic rabbit aorta. The ultrasound image illustrates inhomogeneities in arterial wall thickness, the strain rate
indicates the arterial segment with reduced elasticity and the spectroscopic photoacoustic image illustrates the
accumulation of lipids. The results demonstrated that ultrasound, strain rate and spectroscopic photoacoustic imaging are
complementary. Thus the integration of the three imaging modalities advances the characterization of atherosclerotic
plaques.
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